The damage to West Antarctica occurs under the massive glacial ice platforms from the warming of the Southern Ocean's Circumpolar Deepwater (CDW) spilling onto the continental shelf via seabed troughs has been documented in recent years.
Troughs differ from ocean trenches, which are long and deep like a canyon. A trough is also long but shallower and shorter, and the ocean bed topography is not as extreme; it is more like a basin below the ice shelf, such as Thwaites or Pine Island Glacier. The inflow of warm water is delivered by an eastward, subsurface slope current called the Antarctic Slope Undercurrent, which resists westward momentum generated by wind and tides.
The rapid melting of the glaciers' bottom ice is alarming. Still, this relatively recent phenomenon remains the "mechanism via which the undercurrent forms, and thus what controls the shoreward heat transport, remains unclear."
A new study from researchers specializing in mathematical models and oceanography models, Yidongfang Si, Andrew L. Stewart, Alessandro Silvano, and Alberto C. Naveira Garabato, found that the steering of the undercurrent is the meltwater from the massive ice cavities carved by warming waters decaying the ice, a result of greenhouse gas emissions from human activity. Increasing melt at the bedrock strengthens the Antarctic Slope Current melt, amplifying the Circumpolar Deepwater delivery to the ice. The study argues that it indicates positive feedback likely to accelerate the melting of the ice shelves, weaken an already threatened Amundsen Sea Embayment, and further destabilize the highly vulnerable West Antarctica Ice Sheet.
Melting ice represents up to 25 percent of today's sea level rise. If you have read this far, you are astonished by the level of complexity in this process. I doubt we have a solution for reversing or slowing Earth's most substantial current (Antarctic Circumpolar Current (ACC)), particularly the change in the slope current meltin ice.
Observe the eddies and swirls in the current, which are changing ocean dynamics in the Amundson Sea and driving warming water much closer to the ice. This is vorticity, and the physics has changed due to meltwater creating tunnels in the ice in dangerous feedback.
From the University of South Hampton presser.
It's known that Circumpolar Deep Water (CDW), a water mass that is up to 4°C above local freezing temperatures, is flowing beneath the ice shelves in West Antarctica and melting them from below. Since so much of the West Antarctic Ice Sheet lies below sea level, it is particularly vulnerable to this warm water intrusion and may further retreat in the future.
Previous observations and models have revealed that eastward undercurrents are transporting this warm water to cavities under the ice shelves. Despite its significance, the mechanism driving this undercurrent has remained elusive.
Professor Alberto Naveira Garabato, from the University of Southampton, a co-author of the paper, said, "Our findings suggest a positive feedback loop: as the ice shelf melts more rapidly, more freshwater is produced, leading to a stronger undercurrent and more heat being transported toward the ice shelves."
Dr. Alessandro Silvano from the University of Southampton, a co-author on the study, said, "These simulations reveal that this deep current conveying warm waters toward the ice shelves is driven by the very same ice shelf melting that such warm waters cause."
Their models suggest that when the warm CDW interacts with the ice shelf, it melts the ice and mixes with the lighter, melted freshwater.
This water then rises through the layers of water above it. As it does, it spreads out and stretches the layer of CDW vertically. This stretching creates a swirling motion in the water.
If there's a trough (a kind of underwater valley) near the coast, this swirling motion is then carried away from the ice shelf cavity toward the edge of the shelf by the movement of pressure within the water. This movement helps drive a current along the slope of the seafloor, directing more warm water toward the ice shelf.
The underwater current forms a bit farther away from the ice shelf, so as more ice melts, the current gets stronger, carrying even more warm water toward the ice shelf.
Dr. Silvno pointed out that the marine extension of massive West Antarctic glacier cavities is not currently being taken into account in climate models.